Simple recursion example

Python/028_recursion.py

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+# A simple demonstration of recursion
+
+# Recursion is the act of calling a function from
+# within itself. This is not often used, but super
+# handy for doing mathmatical work and walking
+# directory structures in a file system.
+
+# In this example we will recursively calculate the
+# factorial of a number. If you will remember from math
+# class a factorial is all the numbers from one to a
+# specified number multiplied together.
+# i.e 6 factorial is 1 * 2 * 3 * 4 * 5 * 6
+
+# This is the recursive function.
+# It returns the parameter if it equals one
+# Otherwise it multiples the parameter by the results of
+# calling the function with the parameter reduced by one
+def factorial(n):
+    if n == 1:
+        return n
+    else:
+        return n * factorial(n-1)
+
+num = None
+while num is None:
+    try:
+        num = int(input("Enter a positive number: "))
+        if num < 0:
+            num = None
+    except:
+        pass
+
+if num == 0:
+    print("Factorial of 0 is 1")
+else:
+    print(f"Factoial of {num} is", factorial(num))